U.S. patent number 6,031,505 [Application Number 09/105,354] was granted by the patent office on 2000-02-29 for dual embedded antenna for an rf data communications device.
This patent grant is currently assigned to Research In Motion Limited. Invention is credited to Krystyna Bandurska, Peter J. Edmonson, Robert A. Grant, Perry Jarmuszewski, Yihong Qi, Lizhong Zhu.
United States Patent |
6,031,505 |
Qi , et al. |
February 29, 2000 |
Dual embedded antenna for an RF data communications device
Abstract
An RF antenna system is disclosed having at least one meandering
antenna line with an aggregate structure formed to substantially
extend in two dimensions, to effectively form a top-loaded monopole
antenna. The meandering antenna line includes at least one
localized bend for providing a compressed effective antenna length
in a compact package. The present antenna can be made as an antenna
system having discrete transmit and receive antenna lines, so as to
form a dual antenna system. The localized bends on each line
electromagnetically couple with the respective bends on the other
line, thus increasing electromagnetic coupling efficiency, thereby
increasing antenna bandwidth and gain.
Inventors: |
Qi; Yihong (Waterloo,
CA), Jarmuszewski; Perry (Guelph, CA), Zhu;
Lizhong (Waterloo, CA), Edmonson; Peter J.
(Hamilton, CA), Bandurska; Krystyna (Waterloo,
CA), Grant; Robert A. (Guelph, CA) |
Assignee: |
Research In Motion Limited
(Waterloo, CA)
|
Family
ID: |
22305341 |
Appl.
No.: |
09/105,354 |
Filed: |
June 26, 1998 |
Current U.S.
Class: |
343/795; 343/725;
343/729 |
Current CPC
Class: |
H01Q
1/243 (20130101); H01Q 1/36 (20130101); H01Q
1/38 (20130101) |
Current International
Class: |
H01Q
1/36 (20060101); H01Q 1/38 (20060101); H01Q
1/24 (20060101); H01Q 009/28 () |
Field of
Search: |
;343/795,702,7MS,725-730 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wong; Don
Assistant Examiner: Nguyen; Hoang
Attorney, Agent or Firm: Jones, Day, Reavis & Pogue
Meyer, Esq.; Charles B.
Claims
We claim:
1. A dual antenna system for an RF data communications device,
comprising:
two physically-separated, but electroctromagnetically-coupled
meandering antenna lines, wherein one of the meandering antenna
lines forms a receive antenna and the other meandering antenna line
forms a transmit antenna,
each of the receive and transmit antennas having an aggregate
structure formed so as to substantially extend in two dimensions,
thereby forming a top-loaded monopole antenna,
wherein each meandering antenna line includes at least one
localized bend, the localized bends of the two antennas being in
close physical proximity to each other in order to
electromagnetically couple the transmit antenna to the receive
antenna.
2. The dual antenna system of claim 1, wherein the meandering
antenna lines are formed onto a flexible substrate and affixed to a
rigid dielectric retainer.
3. The dual antenna system of claim 1, wherein each respective
antenna line is tuned for a separate bandwidth.
4. The dual antenna system of claim 1, wherein at least one of the
antenna lines further comprises at least one high current portion
for reducing interference from close proximity metal
components.
5. A dual antenna system for an RF data communications device,
comprising:
a receive antenna comprising a first meandering line having an
aggregated structure formed so as to substantially extend in two
dimensions, wherein the first meandering antenna line includes at
least one localized bend; and
a transmit antenna comprising a second meandering antenna line that
is physically separate, but electromagnetically-coupled to the
first meandering antenna line, the second meandering antenna line
having an aggregate structure formed so as to substantially extend
in two dimensions, wherein the second meandering antenna line also
includes at least one localized bend in physical proximity to the
localized bend of the first meandering antenna line so as
electromagnetically couple the two meandering line antennas.
6. The dual antenna system of claim 5 wherein each respective
antenna line is tuned for a separate bandwidth.
7. The dual antenna system of claim 5 wherein the meandering
antenna lines are formed onto a flexible substrate and affixed to a
rigid dielectric retainer.
8. The dual antenna system of claim 5 wherein at least one of said
antenna lines further comprise at least one high current portion
for reducing interference from close proximity metal
components.
9. An antenna, comprising:
a transmit antenna line having a localized bend, wherein the
localized bend includes a length of antenna line that is nonlinear;
and
a receive antenna line including a localized bend, wherein the
localized bend includes a length of antenna line that is
nonlinear;
wherein the transmit antenna line and the receive antenna line are
physically separate from each other, but are
electromagnetically-coupled by positioning the localized bends of
the transmit and receive antenna lines in close physical proximity
with each other.
Description
BACKGROUND OF THE INVENTION
The present invention is directed to the field of antennas used for
RF data communications devices, particularly those used to transmit
and receive digital signals, e.g., two-way pagers and the like. The
antennas used with previous RF data communications devices are
prone to significant problems. Many previous pagers are "one-way"
pagers that are only able to receive a pager signal. However, many
factors can contribute to the loss of an incoming message signal.
Thus, it is desirable to employ a "two-way" pager that sends an
acknowledgment signal to the remote station to confirm receipt of a
message or to originate a message.
In previous VHF one-way pagers, it had been common to use a
loop-type antenna, which is effective at receiving signals in the
presence of the human body, which has properties that tend to
enhance VHF radio signals. However, loop-type antennas are poor at
the UHF frequencies needed for two-way pagers. Also, such antennas
are typically embedded in a dielectric plastic pager body, which
reduces the effective bandwidth of the received signal. Such a
configuration has a very narrow bandwidth of typically about 1%.
Such antennas also have poor gain performance when transmitting a
signal, and are thus not useful for a two-way pager design.
Many previous two-way telecommunications devices use a "patch"
antenna, in which a large, flat conducting member is used for
sending and receiving signals. Patch antennas permit two-way
communication under certain narrow bandwidth conditions, but do not
provide a desirable radiation pattern. Signals propagate
perpendicular to the flat surfaces of the antenna, and so the
acknowledgment signal diverges within a bi-lobed conical envelope
along an axis of propagation. While the signal transmits well "in
front" and "behind" the pager, performance is poor if the signal
axis is not well aligned with the remote station. Also, patch
antennas are large, and can be as large as 16.times.16 cm.sup.2.
While this may be fine for a mobile laptop computer, such is not
well suited for a small hand-held mobile unit such as a pager.
Patch antennas can be made smaller, but at a significant sacrifice
of gain.
An improved two-way pager antenna design is shown in U.S. Ser. No.
08/715,347, filed Sep. 18, 1996, entitled "Antenna System For An RF
Data Communications Device." This design incorporates a dipole
antenna capable of sending and receiving signals having both
vertical and horizontal polarization components, thereby increasing
the likelihood of acquiring the signal. The dipole antenna is
incorporated into the pager lid and anisotropically coupled to the
LCD pager display element. This coupling effect divides the central
frequency into two separate peaks, thereby increasing pager
bandwidth.
While excellent under ideal conditions, the coupling effect varies
as a function of the spatial distance separating the LCD,
variations in the anisotropic composition of the LCD, and ground
planes of the pager circuit boards. As the lid is opened and
closed, antenna gain can vary between 0 to 1 dB and -1 to 0 dB.
Also, as this distance varies, the center frequency changes,
affecting the antenna's very wide bandwidth. These effects tend to
degrade antenna performance in either send or receive modes.
The above-noted design incorporates a RF switch to change the
antenna between transmit and receive modes. This switch is
expensive and very fragile to electrostatic discharge, adding
expense to the manufacture and maintenance of the unit. Also, this
switch is lossy, reducing antenna gain by about 0.5 dB. Further,
with this design, LCD placement with respect to the antenna is
critical, requiring fine tuning and tight manufacturing tolerances,
resulting in labor-intensive (and thus expensive) manufacturing.
Also, with the previous antenna design, impedance matching with the
radio circuit is difficult. Testing the previous antenna is
difficult since it could only be tested in an assembled pager, and
so antenna failures contribute to unit failures during testing.
Also, the antenna tends to interfere with the radio components in
the pager, thereby further reducing performance.
BRIEF DESCRIPTION OF THE INVENTION
In view of the drawbacks and disadvantages associated with previous
systems, there is a need for an RF communications antenna system
that enables reliable two-way communication.
There is also a need for a two-way RF communications antenna system
that provides a uniform radiation pattern within 360 degrees of
azimuth.
There is also a need for an RF antenna system that is insensitive
to variations in environmental conditions.
There is also a need for an RF antenna system that is simple in
construction and can be manufactured with relaxed tolerances.
There is also a need for an RF antenna system that can be easily
tested.
These needs and others are satisfied by the present invention in
which a RF antenna system is provided having at least one
meandering antenna line with an aggregate structure formed to
substantially extend in two dimensions, to effectively form a
half-wave, top-loaded monopole antenna. The meandering antenna line
includes at least one localized bend for providing a compressed
effective physical antenna length in a compact package. The present
antenna can be made as an antenna system having discrete transmit
and receive antenna lines, so as to form a dual antenna system. The
localized bends on each line couple with the respective bends on
the other line, thus increasing electromagnetic coupling
efficiency, thereby increasing overall antenna bandwidth and
efficiency.
As will be appreciated, the invention is capable of other and
different embodiments, and its several details are capable of
modifications in various respects, all without departing from the
invention Accordingly, the drawings and description are to be
regarded as illustrative in nature and not restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a dual antenna system as according to the present
invention.
FIG. 2 is an exploded view depicting the dual antenna system of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
As depicted in FIG. 1, the present invention incorporates an
antenna system including at least one antenna element 12 with a
meandering line structure. The aggregate structure of this antenna
element 12 is formed so that it substantially extends in two
dimensions, effectively forming a half-wave, top-loaded monopole
antenna from a single antenna line capable of transceiving vertical
and horizontal polarization components of a signal. As a further
benefit, this meandering aggregate structure permits the antenna to
have a comparatively long effective length compressed to a smaller
size, e.g., within a pager housing.
As an additional feature, the present meandering antenna line 12
can include one or more extended portions 14, each having one or
more localized bends 16. These localized bends 16 provide further
compression of the antenna length. For example, a 16 cm antenna
(corresponding to the half-wavelength of approximately a 900 MHz
signal) can be preferably compressed in a 8.5.times.6 cm pager body
in the manner illustrated in FIG. 1. In principle, even greater
lengths can be compressed into smaller bodies by increasing the
number of bends 16, providing greatly improved efficiency. The
present design provides excellent radiation pattern
characteristics, providing an omnidirectional "doughnut" radiation
pattern that propagates in 360 degrees of azimuth.
The present antenna system 10 can include a single meandering
antenna line 12, but in the preferred embodiment, the present
antenna system 10 can include plural distinct meandering lines. In
the preferred embodiment, as illustrated in FIG. 1, the present
antenna system includes two meandering antenna lines 12, 22, where
one of the lines 12, 22 is a transmit (Tx) antenna and the
respective other line 12, 22 is a receiving (Rx) antenna. In the
embodiment shown, the line 12 is preferably the Tx line and the
line 22 is preferably the Rx line. The Tx line is preferably
positioned to provide an advantageous transmission pattern with
respect to the geometry of the internal pager components, so as to
insure transmission to the remote station. This permits two
separate narrowband channels to be used for Rx and Tx signals,
rather than one wideband channel, as with the previous single
antenna designs, By providing two center frequencies, the bandwidth
extremities are reduced. Also, each antenna line 12, 22 can
interface directly with the radio circuits, thereby eliminating the
send/receive RF switch used with previous single antennas. In this
way, the present antenna reduced complexity and cost by eliminating
the expensive and fragile switch and the software required to
actuate it. Further, antenna gain is increased, since the switch
was lossy. The antenna lines 12, 22 are coupled to a connector 24,
which includes a matching circuit, and can be formed on the circuit
board. In these ways and others, radio performance is improved with
the present antenna.
The present antenna is also less sensitive to the physical presence
of the operator, since its design, determined by its geometry and
matching circuit selection, will interact with the actual close
pager environment first, and any other ambient interventions
second. This therefore results in a 3 to 7 dB improvement in gain
over previous VHF loop antennas, greatly improving the reception
and transmission characteristics of the system.
Each meandering antenna line 12, 22 includes its own localized
bends 16, 26. In the preferred embodiment, the bends 16, 26 are
placed substantially adjacent. Applicants have observed that, in
addition to providing greater effective antenna length, the
adjacent bends 16, 26 also produce an electromagnetic coupling
effect similar to that discussed in the aforementioned U.S. Ser.
No. 08/715,347, the disclosure of which is hereby incorporated by
reference. The localized bends 16, 26 provide greater concentrated
current per unit length, which affects the coupling coefficient,
permitting more effective coupling with the adjacent line. The
coupling is described in Table 1 as follows:
TABLE 1 ______________________________________ Frequency Coupling
______________________________________ 896 MHz 6 dB 897 MHz 6 dB
898 MHz 6 dB 899 MHz 6 dB 900 MHz 6 dB 901 MHz 6 dB 902 MHz 5 dB
______________________________________
Each antenna line 12, 22 has an associated eigenvector, and without
coupling, these eigenvectors overlap along a common bandwidth. The
coupling effect between the adjacent bends 16, 26 causes a
separation of eigenvectors, in which the eigenvectors split
asymmetrically about a central frequency, resulting in an increased
effective bandwidth for the dual antenna system. Through the
coupling effect, each meandering antenna line 12, 22 has the
effective bandwidth of the coupled system. This coupling is
accomplished without the LCD anisotropic media used in the U.S.
Ser. No. 08/715,347, and so the present invention provides
excellent results without being sensitive to the proximity problems
of the previous device.
As best seen in FIG. 2, the meandering lines 12, 22 of the present
dual antenna system are formed on a flexible substrate, e.g., a
plastic dielectric retainer. The retainer 40 is formed of a plastic
dielectric material which can be easily shaped to create the
desired configuration. Also, the meandering lines 12, 22 can easily
be formed directly on the flexboard 30 by etching a desired pattern
directly onto a copper layer on the flexible circuit board
material. In this way, any desired line pattern can be created
simply and economically, permitting precise control of current
densities along the antenna assembly.
Additionally, the retainer 40 assists in coupling between the lines
due to the dielectric properties of the plastic material. The
retainer 40 also creates a partial barrier between the antenna
system and the pager circuit board, as the dielectric material is
somewhat dispersive of the electromagnetic wave, moving the energy
out of the bandwidth of the radio, and reducing interference.
The retainer 40 also makes the antenna 10 a modular component that
can be easily installed or removed from the pager unit. Also, the
antenna assembly can now be tested as a discrete unit, permitting
the discovery of antenna faults prior to assembly. In this way, the
present antenna assembly improves reliability and reduces the cost
of manufacture by reducing pager unit failures due to antenna
faults.
The present antenna system 10 can also be designed to include a
high current portion 32 to make the antenna insensitive to the
presence of metal components in close proximity to the antenna,
such as metal fasteners and the like. The high current portion 32
is effectively a built-in short circuit that precludes shorts due
to the metal components. This effect is controlled by altering the
effective electrical length of the antenna to create a phase shift
of the antenna structure at the desired resonant frequency. This
phase shift permits the placement of a voltage null, corresponding
to a current peak, at a desired location, thus reducing sensitivity
to metal components. This result can also be obtained and/or
enhanced by adjusting the matching circuits and the meanders in the
antenna lines 12, 22.
The design of the present invention provides an antenna that is
first matched for the physical structure of the pager, i.e.,
batteries, LCD, and radio components. Secondly, the present antenna
is matched for environmental factors such as metal components.
Third, the antenna is matched for impedance with the radio. These
factors result in an antenna that is insensitive to environmental
factors. The present antenna system is easier to manufacture than
previous systems, and requires less critical placement of the
components. Also, since the bandwidth is derived from the coupling
effect, the present invention eliminates the tuning circuits from
the matching networks of previous antennas, thus avoiding the
matching problems encountered with other wide bandwidth antennas.
Further, the tolerances of components in the pager system used with
the present invention are reduced, and construction is
simplified.
As described hereinabove, the present invention solves many
problems associated with previous systems and presents many
improvements in efficiency and operability. However, it will be
appreciated that various changes in the details, materials and
arrangements of parts which have been herein described and
illustrated in order to explain the nature of the invention may be
made by those skilled in the art within the principle and scope of
the invention as expressed by the appended claims.
* * * * *